A shocking number of children have been arrested in connection with sex crimes in the North, with experts blaming online pornography.

In some cases those arrested were as young as six, a Sunday Sun investigation has revealed.

Our probe shows how almost 500 children aged 17 and under were arrested for sexual offences according to police data, 20% of which were formal investigations into reports of rape.

Of those arrested, more than 140 were 13 or younger - with 40 of those being on suspicion of rape.

Charity bosses told the Sunday Sun that they have seen a national trend of an increase in these types of crimes.

One North MP last night said the alarming figures painted a picture of “childhood innocence destroyed”.

However, only a handful of those arrested were convicted of offences. Nationally, only 400 people aged between 10 and 17 were convicted of sexual offences between September 2011 and September 2012.

This amounts to just 7% of the 5,700 convictions for sexual crimes committed by offenders of all ages over the same time period.

This is because a large number of them are below the age of criminality, which in this country is 10, whereas in some cases the accused will have accepted cautions, or the Crown Prosecution Service (CPS) will not have pursued a prosecution.

Experts blamed the shocking figures on the increasing availability of hardcore pornography on phones and the internet.

A spokesperson for the NSPCC said children they work with often appear to be acting out what they have watched.

And young people were more exposed to the “powerful influence” of online pornography than ever before, according to Pat Buckley, NSPCC service centre manager for Newcastle and Middlesbrough.

She said: “There does appear to be a link between incidents of this nature and watching hardcore porn, although more longer term research is needed.

“We should also not forget that the young people perpetrating this serious abuse have often themselves experienced significant emotional deprivation and other forms of abuse.”

While the vast majority of those reported for sexual assault in the North were boys or male teens, a handful were teenage girls. Other offences investigated among the region’s children included making indecent photographs, indecent exposure and incest.

In more than 100 of the incidents probed by police, the alleged victim was 10 or under.

North Tyneside MP Mary Glindon said the Sunday Sun’s investigation, in particular the cases where those arrested had not even reached adolescence, painted a picture of “childhood innocence destroyed”.

Mrs Glindon, who sits on an all-parliamentary party group on body image, argued the mainstream media also had to take some responsibility for the disturbing figures.

“It’s not just the internet,” she claimed. “Even with something as popular as the X-Factor, everything’s so sexual. It leads children into thinking, what’s next? Young children just don’t look like young children anymore,” the Labour MP said.

Simon Hackett is professor of applied social sciences at Durham University.

He has led academic research into children who have sexually abused, and has worked as a practitioner in child welfare. “In my research, 50% of victims had experienced abuse themselves.

“If you’re trying to find trigger behaviour, looking at porn has been a very significant influence.

“Early sexualisation can be a trigger for this kind of offending behaviour.”

Northumbria reported 273 incidents of youths being arrested for alleged sexual assaults against people under 18 over three years, while in Cleveland the figure was 71.

A spokesperson for the force said the number of children under 13 arrested for sexual offences had decreased over the last three years, though figures across the North remained steady.

North Yorkshire reported 79 youths arrested for sexual assault, while Cumbria made 56 arrests. Durham only supplied information for last year, when 22 arrests were made.

Adults who are concerned about behaviour towards a child or young person should call police or social services or contact the NSPCC on 0808 800 5000.

Confidential help for children is available from Childline on 0800 1111.